As someone who reads and writes thousands of developer resumes a year, the major problem I see is that people have a difficult time separating what is important from what isn't, and separating day-to-day responsibilities (which are typically understood from a job title) from unique and novel achievements. I don't know if this kind of tool solves that problem.

Much of my work with resume clients is extracting what they do from them and then putting it into efficient words. Many people struggle with just explaining what they do.

The other problem is that you have to understand that your reader often isn't someone with a highly technical background (or even a recruiting background), so you have to define yourself quickly in order to prevent the reader from misinterpreting who you are. If a reader is looking for a "Python Developer", it's best to refer to yourself that way on the resume.

For senior level people length is often the issue - it's a highlight reel - not a biography. Anyone can get to 1-2 pages max.